Electric multiple motor control system for multiunit printing press drives or the like



y 1954 M. L. PRIBAN 46 ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE l0 Sheets-Sheet 1 Filed Oct. 6, 1951 INVENTOR m Q h F W h 3 3 mm 3 6 III? m2 #2 n NZ s Q Q Q I 5 E WM 5 3E ATTORNEY 1 July 6, 1954 Filed Oct. 6, 1951 Fig.3.

M. L. PRIBAN ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE 10 Sheets-Sheet 2 INVENTOR I MILTON L.' PRIBAN. BY ,4

ATTORNEY July 6, 1954 M, L pRlBAN 2,683,246

ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE Filed Oct. 6, 1951 l0 Sheets-Sheet 3 Fig.4u.

INVENTOR MILTON L. PRIBAN.

ATTORN EY July 6, 1954 Filed Oct. 6, 1951 M. L. PRIB ELECTRIC MULTIPLE MOTOR CONTR AN 0L SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE. LIKE Fig.4b.

l0 Sheets-Sheet 4 INVENTOR MILTON L. PRIBAN.

BY Myth.

ATTORNEY y 1954 M. PRIBAN 2,683,246

ELECTRIC MULTIPLE MOTOR CONTROL, SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE Filed Oct. 6, 1951 10 Sheets-Sheet 5 UIO Fig.5.

INVENTOR BY (Lox E 4,

ATTORNEY MILTON L. PRIBAN.

July 6, 1954 M. L. PRIBAN 2,683,246

ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE Filed Oct. 6, 1951 10 Sheets-Sheet 6 Fig.6c.

INVENTOR MILTON L.PR|BANI BY PM ATTORNEY July 6, 1954 M. L.

ELECTRIC MULTIPLE MOTOR CO Filed Oct. 6, 1951 PRIBAN NTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE l0 Sheets-Sheet '7 FTZ B21 p -1 {ICZ 252 (3C2 1G2 262 n 362 INVENTOR MILTON L. PRIBAN. LAzx z ATTORNEY July 6, 1954 M. L.

ELECTRIC MULTIPLE MOTOR C Filed Oct. 6, 1951 PRIB ONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE l0 Sheets-Sheet 8 Fig. 7.

INVENTOR.

MILTON L. PRIBAN ATTORNEYS y 1954 M. L. PRIBAN 2,683,246

ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE l0 Sheets-Sheet 9 Filed Oct. 6, 1951 iii. 4 1 I m s m f 2 u n m r F r Ill " INVENTOR 9 [13m mus MILTON L. PRIBAN. L MEQL J ATTORNEY July 6, 1954 L AN 2,683,246

ELECTRIC MULTIPLE MOTOR CONTROL SYSTEM FOR MULTIUNIT PRINTING PRESS DRIVES OR THE LIKE oCt- 6, 1951 lo Sheets-Sheet l0 IRSS [I [I H &1

' INVENTOR MILTON L. PRIBAN.

ATTORNEY Patented July 6, 1954 ass sts ELECTRLL ll. SYSTEDI PRESS Mil-ton lL. Priban, (Jlarendon Cline Electric Manufae ULTIPLE BIOTOR CONTROL FOR MUL TIUNIT PRINTING THE HIKE Hills, Ill, assignor to turing Company, Chicago, Ill, a corporation of Illinois Application October 6, 1951, Serial No. 259,146

35 Claims. 1

My invention relates to systems for controlling the speed of a group of mechanically coordinated electric motors and, in a particular aspect, to speed control systems for the jointly operating drive motors of a multi-unit or multi-group printing press or the like plurality of simultaneously working units.

It is an object of my invention to provide a control system in which a single conditionresponsive coritroller determines and regulates the coordinated operations of a group or parallel connected motors and in which the number of motors thus jointly controlled can be selectively varied in accordance with different job require-- ments, for instance, in accordance with the numher or printing press units or groups that are to operate with a folder unit of a newspaper or magazine printing press. It is a more specific object to achieve the just-mentioned perform-- ance with the aid of saturable reactors.

Another object of my invention is to make the current-carrying capacity (or impedance per motor) of such a controller adjustable or controllaole in accordance with the selection of the jointly controlled motors so that the control performance r tive to each operating motor remains unaffected by changes in the number or total power rcquir ments of the selected. motors.

It is also an object of my invention to make the controll r operate, in response to a speed-proportional voltage or other condi ion-responsive signal vo "es, in such a manner that the oontroll 1" will see maintenance of a chosen motor speed regardless of the selected number of jointly speedcontrolled motors.

Still another object, more specific than the forego ng, is to provide a versatile multimiotor centre. system that permits controlling a large number of ilr-line arranged and mechanically interconnectable motors, particularly p sun and folder drive motors of a multi-unit ne -vspaper printing press, in either one or a plurality of motor groups, each group having a selectively i iable number of jointly speed-controlled motors, for instance, a selective number of press root to operate together with one of the remotors of the just-mentioned pr ss drive. My invention also aims at providing a inultimot r conhol system which, while satisfying one of the aforementioned objects, is suit l is for multiphase alternating-current inducti n motors, wound-rotor or squirreh motors, and permits controlling a selected number of such motors to run in parallel at a regulated subsynchronous speed adjustable over a wide range of speed values including, if desired, the low speeds needed in a multi unit printing press drive or the like for inching, threading or accelerating operations.

It is also an object of my invention to incorporate into a multi-motor control system the controls needed for one or more auxiliary motors for inching or threading operations or for breakaway torque, and to make the control performance for the unit drive motors and that for the appertaining auxiliary motor selective and mutually exclusive.

The foregoing and other objects of my invention, as well as its essential features set forth with particularity in the claims annexed hereto, will be understood from the following description in conjunction with the embodiments shown by way of example on the accompanying drawings, in which:

Fig. 1 is a schematic one-line circuit diagram of the main power connections of a motor control system for a multi-unit newspaper printing press drive, while Figs. 2a and 2b, which to he placed side-by-side to form a single illustration and are hereinafter jointly referred to as Fig. 2, show a more detailed three-phase circuit diagram of part of the same system;

Fig. 3 is a schematic one-line circuit diagram of the power connections of a second control system, and Figs. 4a and 4b, to be placed t get-her --ereinafter jointly referred to as l. show a more detailed threephase circuit of part of the system;

Fig. 5 is a schematic one-line circuit diag: the power connections "1 of of a third control system, and Figs. 6a and 6b, to be placed together and hereinafter jointly referred to as Fig. show a more detailed three-phase diagram of part of this system: while Fig. 7 shows a circuit diagram of a modificatio" applicable in systems according to the preceding embodiments.

The control system of Figs. 1 and 2 pertains to the drive of a newspaper printing press itl twelve pres-s units denoted by U! through Ul 2 and two folder units F5 and F2, only the folder units Fl, F2 and the press units UI, U5, Us and Us? with the appertaining components of the control system being shown in the three-phase diagram of Fig. 2. Each of the fourteen press and folder units is driven by an induction motor denoted by M through M52 and FMI, FMZ, respectively. The motors (as well as those in the other or. hodiments) are either of the wound-rotor or squirrel cage types. They are axially aligned so that the appertaining rotor shafts i may be directly in erconnected to equalize the speed of the separate press and folder units. Each rotor shaft drives the appertaining press or folder unit through a bevel or worm gear 2 and a coupling 3. Each shaft 8 is equipped. with a coupling which permits joining the shaft with that of the adiacent motor. Coupling 4 is preferably of the differential type, i. e. its two members are angularly adjustable relative to each other to permit a proper phasing of the rotors.

The just-described in-line arrangement of multiple-unit drive motors is known as such from Patent No. 1,877,387 of A. J. Cline. It permits coupling a selected number of press units with either one of the folders, or operating both folders at the same time but independently of each other, each with a selected group of press units. Of course, the entire line of units may have more than two folders if desired. It will be understood that in each group of units the web to be printed upon passes through the press units and eventually reaches the folder of the group where the webs from the several printing units are reduced to page form. Details of the printing procedure and the appertaining web guide and printing means are generally known and not essential to the present invention so that their further description is unnecessary.

Referring particularly to the basic diagram of Fig. 1, it will be recognized that all motors can be energized from two bus systems BI and B2. bus system is hereinafter referred to simply as bus, although it may be single-phase or multi-phase and hence may comprise a plurality of individual bus conductors. The folder motor FM! is shown. permanently connected with bus Bl while folder motor FMZ is shown in permanent connection with bus B2. Each of motors Ml through Miz is equipped with a switch S1 through Sl2. respectively. The connection of switches S! to S4 is such that each of motors Ml to M6 can be selectively connected to bus B! in parallel relation to folder motor FML Similarly the switches S9 to S!2 permit a selective connection of each of motors M9 to MR2 to bus B2 for parallel operation with folder motors FM2. The switches 85 to S8 are designed as two-way switches so that each of motors M to M8 can be selectively connected either with bus B! or with bus B2.

When any number of motors M l through M8 have been coupled together with. folder motor FM! and thus are mechanically interconnected to operate at the same speed. the corresponding switches are closed so that the operating motors are all connected to the same bus Bi and hence receive all the same terminal voltage. In this manner, the electric energization of these motors is equalized through the connecting bus Bi. The same applies, of course, to the motors that may be mechanicallv coupled at a time with the folder motor FMZ and are energized through bus B2.

Each of buses BI and B2 is connected with alternating-current supply means, such as terminals or mains, through respective voltage control devices which, as will be explained, impress on each bus a variable and regulated potential in response to the speed or another mechanical or electrical operating condition of the group of motors energized from that bus. The voltage control devices, according to a preferred embodiment of my invention, consist of banks of saturable reactors disposed between the current-supply mains Cl, C2 and the buses B! and B2.

According to Fig. 1, two banks of reactors are connected with respective buses Bi and B2. Each bank has a number of reactor units equal to the number of motors that may be selectively connected to the bus appertaining to that reactor bank. The reactor units of the first bank are denoted by El to R4, FE! and IE5, EH6, lRl, |R8 for the respective motors M! to Md, FM! and M5 to M8. The reactor FR! is shown permanently connected between bus Bi and current supply main CI. The other reactor units are connected parallel to reactor FR! through re spective double pole selector switches RS1, RS2, RS3, RS4, E65, EH85, ERS? and iRSB. The reactor bank appertaining to bus B2 is similarly designed, the individual reactor units being denoted by 235, 2R3, 2R3, 2R8, F32 and R9 to RlZ, and the appertaining two-pole switches by 2RS5, EH85, 2RSl, ZRSS, RS9, RS), RSll and RSIZ.

For each number of motors that are to cooperate and to be jointly controlled at a time, the same number of reactors are electrically parallel connected in each bank by closing the corresponding'reactor switches. In this manner, each bank as a whole represents an impedient voltage control device of selectively variable current carrying capacity.

While no selector switches are shown for the two motors FM! or FMZ, nor for the two reactor units FR! or PR2, it will be understood that selector switches may also be provided for these devices in order to increase the flexibility of the control system.

In a control system according to the basic diagram of Fig. 1 each of the current supply means (line terminals L and mains Cl, C2) has a multi-phase design while each reactor unit (or other voltage control device) i either singlephase or multi-phase depending upon the number of phases of the buses Bl, B2. The detailed circuit diagram according to Fig. 2, for instance, shows three-phase motors connected to three-phase buses Bi, B2 and controlled by three-phase reactor units from three-phase current supply mains.

As shown in Fig. 2 for some or the fourteen motors of the printing press drive, the three motor terminals of each motor are connected to the three respective conductors of the threephase buses Bi or B2. Each of the saturable reactor units, such as unit Psi, has a three-phase design, i. e., is composed of three reactor members whose main windings are series connected between the three bus conductors and the three conductors respectively of the appertaining current-supply mains C! or C2. Each reactor unit has a saturable core or a group of such cores and is equipped with one or several saturation control coils. Since such saturable reactors are generally known as such, a detailed description of their design appears unnecessary. It may be mentioned,

' however, that for the sake of simplicity each reactor unit according to Fig. 1 is shown to be equipped with only one direct-current control coil, these control coils being denoted by BC! to RCaFCl, ERC5, lPtCfi, lRC'i, i'RCfi, ZRCS, ZRCB, ZRC'F, 2303, F532 and RC9 to RCIZ, respectively. In the three-phase circuit design of Fig. 2, the three individual control coils RC! of the threephase reactor unit Rl are series connected in a control circuit i6, preferably in parallel relation to a calibrating resistor D1. The corresponcling control windings of reactors R2 to R4 are similarly connected in the same control circuit. The control coils FCI of the three-phase reactor unit FR; are likewise series connected in the control circuit it, again preferably in parallel relation to a calibrating resistor FBI. The same connection used for the control windings and the appertaining resistors, such resistors EDS and ill-t, of reactors [R5 and 138.

The control windings of the reactors pertaining to the second bank of reactors are similarly connected in a second control circuit i it as is apparent in Fig. 2 from the connection shown for the calibrating resistors 2135, 2138, and Di 2 of respective reactors 2R5, 2R3, and R42.

It should he understood that in this and all other embodiments of the invention, the reactor control windings, here shown series-connected with one another, may be parallel connected or may be arranged in a cz: .bination of series and parallel connections, provided the current flowing in each reactor control winding causes the same response of the alternating-current impedance of all simultaneously controlled bani: reactors.

According to a preferred embodiment of the invention, the switches pertaining to each motor and its corresponding reactor unit are mechanically or electrically interconnected to operate simultaneously or as a single unit. For instance, the switch Si (Fig. 2) for connecting motor Mi to bus Bi, and both poles of switch RSI may be joined to form part of a single contactor, this being schematically represented by a orokendine connection S. It then merely necessary to close a single selector switch for connecting the desired motor to the proper energizing bus for also adapting the current capacity of the corn trol reactors to the proper value.

The speed of any selected group of motors joined to the same bus depends upon the terminal voltage applied to that bus. This bus volt age is determined by the voltage drop, and hence by the effective reactanoe, of the appertaining reactor bank. The effective reactance of each bank. is controlled by the premagnetization pro vided by the saturation control coils of the individual reactor units. When the premagnetization is a minimum, the reactor cores are unsaturated so that the effective reactance of each reactor and of the entire bank is high, and the bus voltage is a minimum. When the reactor control coils provide a high prernagnetizing field, the reactors become saturated during the period of each current wave to a-. extent depending upon the degree of preniagnetization and reduce the effective react-ance so that the bus voltage is correspondingly high. Since the reactance windings of all reactors of each bank are tied together in parallel relation and since all appertaining control windings are jointly controlled from the same control circuit H] or i l0, each re actor bani: behaves as a unit so that all motors of a group, in mechanical as well as electrical respects, are forced to behave as a unit and are synchronized at a speed determined by the voltage conditions of the appertaining control circuit ill or HQ.

Due to the fact that each change in the selec tion of cooperating motors is accompanied by the proper capacity adjustment of the control reactors, the control effect is independent of the number of reactors and motors operating a time so that the same voltage of the control circuit !0 or its will always give the same response on the alternating-current side of the operating reactors, thus making the control independent of the number of motors controlled.

The control circuit 59 is energized from the output terminals of a rectifier l2 which is series connected with the alternating-current winding ii of a transfer reactor TRl. Energization for rectifier l2 and winding i i is supplied from mains Ci. The transfer reactor TBS serves as a mixer for the various signal and control voltages in conjunction with rectifier it, represents also an amplifier of the magnetic type. The transfer reactor has a saturable core equipped with pr magnetizing direct-current control coils it, H2, H5 and i 6. Any change in effective reactance of winding ii, caused by a change in the resultant premagnetizing field of coils :3 to Hi, causes a corresponding change the voltage drop impressed on the rectifier and hence pr ortional change of the dir ct-curvoltage pressed on the control circuit Coil 13 receives constant bias voltage from a suitable source of constant voltage. source is exemplified by a rectifier which is energized from mains Cl and impresses its output voltage on a voltage dividing resistor Soil hi r ceives adjustable pattern voltage from across a selectively adjustable portion of a potentiometer rheostat is impressed by constant voltage from the rectifier l7. Coil iii receives the condition responsive signal voltage. In this embodiment. the signal voltage is supplied f om a tachometer generator FT! mounted on shaft 1 of folder inotor FMi. A calibrating resistor 2'3 may be interposed if necessary. If motor FM! is a woundrotor inotor, then a signal volt may be derived from the secondary motor circuit to excite coil 15 in dependsce upon the s frequency of the motor. Coil 15 receives a is "lhack voltage from across the output terminals of rectifier l2 preferably through a calibrating resistor 2 i. The voltage feedback to coil is may be adjusted to supply most of the premagnetization needed for any operating condition of the transfer reactor so that the coils l4 and i5 are called upon only to supply the additional stimulus needed to shift the operating condition of the transfer reactor in accordance with the change of voltage needed in circuit 10 to maintain the met r speed at a desired value. This value is adjusted by the slider setting or" control rheostat is. When the motor speed is in accordance with the value adjusted at rheostat iii, the excitation of coil i4 is approximately balanced by the speed responsive excitation of coil 15. When the motor speed departs from the desired value, the resultant premagnetizing field of coils is and it assumes a value of the polarity and magnitude needd to restore the proper speed. The excitation of winding l3 depends upon material and design features of the transfer reactor remains constant during the operation. Under certain con ditions such a separate may not be necessary.

It will be understood that, if desired, he various premagnetising control windings or fer reactor TRI may be combined or to obtain a smaller number correspondingly joining the excitation circuits. Since the is essentially a magnetic the various magnetic and electric circui modifications well known from magnetic amplifiers may be en ployed instead of the, one here exemplified.

The control circuit ii!) for the second reactor bank is energized through the alternating-curoi windings by pertaining el ctric ti .lnsier reactor rent winding ill of a transfer reactor TRZ and a series-connected rectifier I ii in the same manner as described with reference to control circuit It and transfer reactor TRl, except that the control coils H3, H5, H5, N of reactor 'I'RZ are energized from respective voltage supply means that receive excitation from the mains C2 or from system components relating to bus B2 and folder motor FMZ. For instance, coil H5 is connected (not shown) with a tachometer generator FIQ joined with motor FMZ, while coils 1 it, i i i, 2 it are energized in a manner analogous to the energization of coils #3, it: and i5, respectively.

A reactor control system of the type described affords a wide range of speed control. If desired, this range can be extended down to the low creeping speeds needed in printing press operation for threading, inching or break away torque. This has the advantage that the same induction motors that operate the printing press system under normal printing conditions may also serve for the just-rnentioned slow speed operations thus making it unnecessary to equip the system with separate inching motors.

It will be understood that such a wide range of speed control requires correspondingly large reactors. However, a system of this type also lends itself to the provision of one or more separate inching motors as known from Patent 2,211,002 or A. J. Cline. Such a small auxiliary motor is preferably joined with the shaft of each folder motor. It may be equipped with a reactor type control interlocked with the main motor control and, as a rule, requires an only limited speed range since inching speeds are necessarily single speed adjustments. An example of such an auxiliary control with its appertaining control and interlock components is embodied in the system shown in Figs. 3 and 4 and described presently.

The multi-motor control system according to 3 and a is also designed for a printing press drive with twelve press units and two folder units each having an appertaining alternatingcurrent motor of the induction type. In the basic system diagram of Fig. 3, the units and motors are denoted by the same respective reference characters as in Fig. 1. All motors are axially aligned and interconnectable by couplings in the manner described previously. According to Fig. 3, however, the system is further equipped with two auxiliary motors AME and AMt. Motor Alvll, as shown in Fig. 4, can be coupled by means of a coupling [83 and a gear N32 with the shaft l of folder motor Flvil. The second auxiliary motor AM2 (Fig. 3) is similar- 1y connectable with the shaft of folder motor FMZ. Each of these auxiliary motors serves to operate the appertaining folder and press group at a slow speed for threading or inching purposes or to provide breakaway torque at the start of the printing operation.

As in the first-described embodiment, the system according to Fig. 3 has two buses Bl, B2 which are energized from respective supply mains C 1, C2 and are connected with these mains by saturable reactor units denoted by R! through R52, FE! and PR2. The folder motor FM! is shown to be permanently connected to bus El, and the appertaining reactor FR! is permanently connected between bus Bi and main CI. Motors Ml to Md and the appertaining reactors R! to R6 are provided with selector switches S! to S4. When any one of these switches is closed, the

elO

appertaining motor is connected to bus Bi, and the appertaining reactor unit is connected to supply main Cl. Motors M5 to MIE and the appertaining reactor units R9 to Hi2 have respective selector switches S9 to SlZ which permit connecting any one or several of these motors to bus B2 while closing the reactor circuit between bus B2 and main C2.

The intermediate motors M5 to M8 and the corresponding reactor units R5 to R8 are equipped with two-way selector switches S5 to S3. These switches permit connecting any one or more of these motors to either bus Bl or bus B2 while simultaneously connecting the corresponding reactors to the proper current supply mains Cl or C2.

With such an arrangement the two banks of reactors overlap and include a number of reactor which can be selectively grouped into one or the other bank. The number of individual reactor units needed in this system is equal to the number of motors.

The detailed diagram of a three-phase bus and three-phase reactor connection according to the schematic diagram of Fig. 3 is shown in Fig. 4 for three of the fourteen motors of the system. Each of buses Bi and B2 comprises three conductors, one for each phase, and each reactor is composed of three members, one for each phase. The appertaining two-pole switches are correspondingly given a three-phase design. For instance, switch Si has three contacts 3i which, when closed, connect the terminals or" motor Ml to the three conductors of bus Bi and three contacts 32 which then connect the terminals of the reactor unit Rl to the three main conductors Cl. Switch Si, as exemplified, is designed as an electromagnetic contactor whose coil 33 also actuates a selfealing contact 35 and is energized from a suitable source DC under control by a normally open On contact and a normally closed Off contact both preferably of the push button type. When motor Ml is to be selected for operation, the actuation of contact 35 causes switch Sl to close and to stay closed until contact 35 is opened by the operator. It will be understood that the switches S2 to St and S9 to EH2 (Fig. 3) are similar to the switch Si just described.

Each of the two-way selector switches S5 to S8 may be designed and connected as shown in Fig. 4 for the switch appertaining to motor M and reactor R6. Instead of using a single twoway switch S6 as schematically indicated in Fig. 2, this switch is preferably composed of two electromagnetic contactors i553 and 2S5 (Fig. 4) which are mechanically or electrically interlocked so that only one of them can be closed at a time, an electrical interlock being illustrated in Fig. 4. The contactor 1S5 has three power contacts ll which when closed connect the three motor terminals with the respective three conductors of bus Bl. Three further contacts 52 of contactor lSt then connect the three phase members of reactor unit R5 to the three conductors of mains CI. Contactor lSEi is also equipped with a normally open self-sealing contact it and a normally closed interlock contact 44, all contacts being controlled by a contactor coil i5 which is energized under control by a normally open On contact is and a normally closed Off contact ll from a suitable current source D. C.

The source DC may be identical with the source D. C. for energizing the above-mentioned contactor coil 33 and with all other sources denoted by DC in Fig. 4. For that reason, all of them are identified by the same reference character. While these sources (or single source), for convenience and lucid illustration, are represented by the symbol of a direct-current battery, it will be understood that any available supply means of substantially constant voltage may be used, such as a rectifier circuit energized from the alternating-current line that energizes the entire control system.

The second contactor 2S6 has contacts I4] to its which correspond to the respective contacts ii to 44 of contactor lSE and are all controlled by a coil [45 energized through an On contact 546 and the abovernentioned On contact 41. Contactor 286 is further equipped with control contacts 148, 149, I59, whose purpose will be explained in a later place.

When the motor M6 is to be energized from bus Bi to make the press unit UE cooperate with folder Fl, the On contact 46 is depressed by the operator. This energizes coil 45 which closes the main contacts 4|, 412 of contactor [S5 and establishes at contact 43 a sealing circuit so that contactor 1S5 remains thereafter closed until the Off contact 4? is actuated by the operator. The energizingcircuit of coil 45 extends through the interlock contact 144 of contactor 2S6. Consequently, contactor IS6 can be closed only when contactor 2S5 is open. If motor lvlt is to be connected to bus B2 for joint operation with the motor of folder F2, then the contact P36 is to be actuated so that contactor 286 will pick up. Since the circuit of coil 145 extends through the interlock contact 44 of contactor 1S3, contactor 285 will pick up only when contactor 556 is in the illustrated open position.

The reactors of the control system are designed and operative in the same manner as described with reference to the embodiment of Figs. 1 and That is, the reactor control windings such as the windings RCi of the three-phase reactor R5, the control winding FCi of the reactor Fill and the control winding RC6 of reactor R8 are all series connected in the above-mentioned common control circuit i8, preferably each threephase group of control windings being paralleled by a calibrating resistor such as those denoted in Fig. 4 by Di, FD; and The control circuit it forms a closed loop energized from the direct-current terminals of a rectifier l2 which is series connected with the main winding ii of a transfer reactor TR! across two conductors of the alternating-current supply mains CE. The transfer reactor TRi direct-current control coils i3, l-l, IE, it and serves as a mixer and amplifier basically in the same manner as the transfer reactor TR! in the above-described system of Fig. 2. The voltage drop impressed across the input terminals of rectifier !2 depends upon the effective reactance of winding 1 i which, in turn, is controlled by the resultant effect of the preinagnetizing excitation impressed on coils 3 to it. As a result, the excitation of the control coils RCi, etc. of the in in reactors and hence the effective reactance of these main reactors and the terminal voltage impressed on the appertaining bus Bi are also under control by the premagnetizing control excitation of the transfer reactor TR! (see Fig. 4a)

The control circuit lid for the reactors of the motor group connected to the bus B2 is designed and operative in the same manner. This circuit is energized from a rectifier H2 in series conof reactors controlled l0 nection with the main winding 1 a i of a transfer reactor TR2 whose preniagnetizing control coils H3 to H5 correspond to the above-described coils E3 to H5, respectively.

Since each of the motors M5 to L3 with the appertaining reactors R5 to R8 nected selectively to either bus Bi or bus E2, the system is so designed that the control cells for the reactors appertaining to these motors are also selectively energized other from control circu-.-

or from control circuit iiii, depending upon whether the particular root-or is energized from bus Bi or from bus 132. The re ans for s :uring such selective excitation of the r dings are illustrated in Fig. A

actor control wi or motor M6 and reactor unit Assume that -c.ntactor E o closed so that motor g from Bi. Then the ccntr i and 2 39 are in the l connect the reactor co' J'rol windings with the appertan: ng calibrating shunt resistor D6 across points P! and ?2 of control circuit ill. Consequently, the reactor con 'ol coils wtih re sister are new series conne N1 the circuit it in the same manner for lnste' c contacts ustrated positions and Love the

control coils RCi and FCi with the appe respe ive resistors Di and F53. At the same time, the contacts and is; connect a resi tor across points PS and P of the control c uit H6. The resistor E5 has the same ohmic value the parallel combination of col ol coils R5 and resistor D8 and has the same time constant as this combination. Consequently, when the motor is energized from bus Bi and the control windings Rt are connected in the control circuit the control circuit lie nevertheless completed through the resistor and the total impedance and time constant of each control circuit are independent or" the selected number by the circuit at a time. On the other hand, when the contactor 285 is closed to operate motor ME together with folder motor FMZ, then the cont cts is? and M3 are lifted and connect the reactor control windings R6 with resistor 336 between points P3 and P of control circuit Hi3, while now the resistor E5 is connected through lifted contacts 550 and i5! between points Pi and P2 of control circuit l0. Consequently, any selective connection of motor M's to bus 13! or bus is accoinpanied by a. corresponding insertion of the appertaining reactor control windings into the proper one of the two reactor control circuits.

The selector switch means for motors M5, M7,

M8 are designed and connected in the same anner as the just-described switch mea or motor M5. The two-way selector contacts correspond-- ing to contacts i l-S to it?! in Fig. 4, or course. may be joined with either one of the two contactors Of these switch means for instance, these contacts may be located in contactor 2756 instead of in contactor 286.

While the transfer reactor TRE he controlled in the same manner as in the system of Fig. the system shown in Fig. 4 incorporates a preferred embodiment of the transfer reactor control which will be described presently.

Control coil 13 of transfer reactor T. is energized through a rectifier I! and a potentiometric resistor is from mains Cl to provide a sui able bias voltage of constant value. Control coil it is energized from the output terminals of a rectifier 22 through a speed control rheostat 23. Rectifier 22 is inputwise connected across the bus conductors Bi and hence impressed the motor terminal voltage. Consequently, the excitation of premagnetizing control coil I4 is dependent upon the control eifect of the system so that the control is essentially a terminal voltage feedback. Coil i5 is energized from a current transformer 2d through a rectifier 25 and a voltage-dividing resistor 25. The current transformer 24 is coupled with the supply mains Ci so that the voltage impressed on control coil 56 represents a load current feed-back. Coil i5 is energized from a tachometer generator F'Ti which is driven from the shaft of folder motor MFl (see Fig. la)

The control performance in the just-described reactor connections is primarily determined by the voltages impressed on coils i3 and Hi. When the speed of the motors simultaneously energized from bus Bi has the desired value, the premagnetizing excitation jointly provided by coils i3 and id is approximately balanced. The speed value at which this balance occurs depends upon the setting of the control rheostat 23. When this setting is changed, the proportion of bus voltage applied to the coil it changes so that now the just-mentioned approximate balance occurs at a higher or lower motor terminal voltage and hence at a correspondingly higher or lower motor speed. The rheostat 23 thus permits adjusting the speed of the co-acting motors to a desired value within the available speed range. The current feed back voltage impressed on coil i6 and the speed responsive voltage impressed on coil l5 have essentially modifying effects. Particularly the speed responsive voltage in this system is needed .only for stabilizing purposes. Consequently, only a very small tachometer generator Fli is required as is more fully explained in the copending patent application Serial No. 250,082, filed October 6, 1951, of H. R. Behr, assigned to the assignee of the present invention.

The control circuits for transfer reactor TRZ are not illustrated because they are identical with the just described circuits for reactor TR! except that they receive energization from components active or energized, together with the folder motor FM? (Fig. 3), bus B2 and supply mains C2.

As mentioned previously, an auxiliary motor Alvii or AM! is provided in each group of drive units for inching and other slow speed operations. Each auxiliary motor has its own control means, those for motor Alvii being illustrated in Fig. l. The terminals of motor AM! are connected through the main windings of a control reactor AR! to the line terminals Ll, L2 and L3 of mains C5 under control by a selector switch SAL This selector switch is interlocked with the main switch lJiCi of the supply mains Cl. Switch MCi has a control coil 52 energized from source D. C. through a normally closed Oif contact 53 and a normally open On contact 55 the latter being connected parallel to a normally open self-sealing contact 55 of switch M01. The circuit of coil 52 extends through a normally closed interlock contact 53 of contactor SAI. Contactor sea has its coil 5? energized from source DC. The coil circuit extends through a normally closed interlock contact 58 of the main switch MCi and through a manually actuable inch contact se. Contactor SAl has three contacts series connected with the respective three main windings of the reactor unit AR! and has a normally open auxiliar contact 5i which controls the direct-current circuit of the premagnetizing control coils 54 of reactor unit ARI.

uring normal printing performance, the main switch MO! is closed and the appertainin interlock contact 58 open. Consequently, the circuit of contactor coil 5? is interrupted so that the auxiliary motor AlJii cannot operate. On the other hand, when switch MCi is open and the main drive system deenergized, the closing or" inch contact 59 causes contactor SA! to pick up and to energize the auxiliary motor AM! to operate at a slow speed determined by the prerragnetizing excitation of control coils ihis excitation depends upon the differential resultant of two control voltages. One of these voltages is normally constant and taken from across a portion of a potentioinetric rheostat '55 energized from a constant-voltage supply DC. The other control voltage is variable and supplied from the tachometer generator FT i The auxiliary motor AME is equipped with a similar control system (not shown) except that it is connected with the line terminals of supply mains C2 and interlocked with the appertaining main switch M02.

The system shown in Figs. 5 and 6 is designed for twelve press units Ui to Hi2 and two folder units Fl, F2, with corresponding drive motors M3 to lVfi2, Phil and Fllfi, in the same manner as the systems described previously. The press motors M5 to M! 2 are connected through respective selector switches Si to Si? with two buses Bi and B2 so that any one of motors Ml to M l can be energized from bus Bi, and any one of motors M9 to l-lii'z can be energized from bus B2, while any one of motors M5 to M3 can selectively be energized from either bus Bl or bus B2. The folder motors Flvii and FMZ are shown to be permanently connected to buses Bi and 32 respectively, although, if desired, the motors FM! and FMZ can also be supplied with selector switches in order to increase the flexibility of the system.

While as far as described the power connections of the system are similar to those of the preceding embodiments, the control system of Figs. 5 and 6 differs essentially in that the voltage control means for each of the two buses consist of a single, though possibly multiphase, reactor unit of the saturable type which is serially subdivided has taps connected with a selector switch. Each reactor unit is of sufficient current capacity to provide power for the maximum number of motors which it may have to control. Referring to Fig. 5, the reactor Gl appertaining to bus Bi has a main winding section iii of a current capacity sufficient for controlling all nine motors Mi to MS and Fl/Ii that may possibly be connected to bus Bi at a time. When a smaller number of motors is connected to this bus, one or several additional reactor sections, such as winding sections ii and i2, are switched in series with the main win -ing section is of reactor GE so that the total reactor impedance for any given state of saturation is increased and thus adapted to the smaller number of motors to be simultaneously operated.

The reactor selector switches GS! and GSZ may be mechanically or electrically joined with the motor selector switches S! to S8 and S5 to S12 respectively so that any motor selection is automatically accompanied by a corresponding adaptation of the reactor units.

It will be understood that instead of using a single reactor coil with a tapped winding, several individual coil or reactor units can be series conof Figs. 1 and 2.

nected with one another to secure the same results.

Referring now to the detailed three-phase circuit diagram of Fig. 6, it will be recognized that each of the hree conductors of bus B! is connected throu a main reactor coil IGI, ZGl or 3G! with a re ctive one of the three conductors of current so; ply mains Cl. Each individual phase reactor has a control coil iCi, 2C! or SCI. The three control coils are series connected in a control circuit iii energized from a rectifier !2. The input circuit of rectifier i2 is series connected with the main winding H or a transfer reactor TR! across the current supply mains. Transfer reactor Tl i and rectifier i2 operate as an amplifying mixer. Reactor TR! has four control coils i3, l4, l5 and i6. Coil 13 supplies a constant bias and is energized from a rectifier I! through a voltage dividing resistor 53. Coil 54 receives adjustable pattern voltage from a control rheostat iii wh ch is also energized by constant voltage from rectifier ll. Coil I6 is supplied with variable signal voltage from across two of the conductors of bus '3! through a rectifier 22 and, if needed, through a calibrating resistor iii. The excitation of the premagnetizing control coil it is proportional to the terminal voltage of the group of root s to be controlled and is poled to oppose "k emagnetizing excitation of the tage from tachometer generator FT! connected with the folder motor FM: preferably through a calibrating series resistor 20. The con rol performance of the transfer reactor TB! is in accordance with that of the corresponcb ing transfer reactor in the above-described system As in the embodiments previously described, the transfer reactor may be replaced by a magnetic amplifier and mixer circult of different design or by some other amplifying device. The individual control circuits of the transfer reactor or amplifier, of course, may also be modified in various ways, and the resultant response can be made dependent upon any suitable operating condition of the folder motor or of the group of simultaneously operating motors to be controlled or regulated.

The 1 'ndings [G2, 2G2, 3G2 of the threephase reactors appertaining to bus B2 are seriesocnnected between the conductors of bus B2 and the respective conductor of mains C2. The appertaining reactor control coils 02, 2C3, 302 are series connected in a control circuit l 10 which is energized from a rectifier H2 whose energization is controlled by a transfer reactor PR2 in the same manner as that of the reactor TRI except that the control voltages are derived from system components associated with the group of motors to be simultaneously energized from bus B2. The individual circuit elements denoted by Hi through 922 correspond to the abovedescribed elements is to 22, respectively.

Mains Cl and C2 are preferably separately energized from an alternating-current line through respective switch and protective devices, only the appertaining main switches MC! and MC2 being schematically illustrated in Fig. 6.

The modifications apparent from the embodiment of Fig. 7 is applicable in the basic system according to Fig. l or in the system according to Fig. 3. As shown in Fig. 7, two conductors 8i and $2 of the supply mains CI are directly connected with respective two terminals of each of the appertaining motors when the motor selector switch, such as switch Si or FSI, is closed. The

Coil iii is provided to supply a remaining main conductor 83 is connected with a single conductor bus B! through voltage control devices designated as saturable reactors of the type described previously. Fig. 8 shows only the folder motor FM? and one press motor Mi of the group of motors energizable from bus Bi. As exemplified in Fig. 7 for the reactor Ri of motor Mi, each reactor has a three-legged saturable core Sill with two control coils 2i and 92 on its center leg.

Coil 5i receives constant bias excitation from across a portion or a voltage dividing resistor S3 energized from a suitable source DC of constant direct voltage. Coil 92 is parallel connected to the corresponding coils of the other reactors and is excited b variable voltage from a mixeramplifier which, in this embodiment, comprises an amplifying dynarnoelectric machine AC whose constant speed armature 9 is connected to the circuit of coil $2 to impress it with variable voltage controlled by a group of field windings, four of such windings, denoted by 95 to being illustrated although amay be used. Field winning is self-ex ted and shown to be series connected with the armature 24. Field winding 99 receives constant but selectively adjustable pattern voltage from control rheostat energize-:1 from the source The selected slider setting of rheostat 95 determines the speed at which the motors energize through bus Bl are supposed to run. Field winding 2'. is exc'ted by feed back voltage taken from across main conductor 33 and the bus conductor, this voltage representing the impedient voltage drop across the bank of active reactors pertaining o bus Bl. it is, of course, also possible to derive the voltage feed back excitation from across bus BI and main conductor Si or 82, provided the field winding 9? is properly poled. Field winding 58 receives a stabilizing speed feed-back voltage from a tachometer generator FTi connected with the shaft of the folder motor Pix fl.

The resultant field of windings iii is always opposed to that of the pattern held a nding and an approximate balance exists during normal steady-state perfo name as is well known for dynamoelectric ampnners. It will be understood that an amplifier of this type may also be used in the other embodiments of the invention instead of the transfer reactors previously mentioned and that, if desired, systems according to Fig. 7 may be equipped with inixer-ampiiriers other than of the dynamoelectric type.

Power connections and power control device of the kind shown in Fig. '7, of course, are equally well applicable in control systems whose basic design corresponds to 5, except that then only one voltage control unit, such as a saturable reactance device, with several series-arranged sections is provided instead of the parallel operating control units shown in Fig. '2.

Generally, a system in which, as shown in Fig. 7. the buses and power control units have a smaller number of phases than the current supply means requires a smaller number of poi-yer control units a s" aller aggregate amount of material for the snare group of units than an otherwise similar system whose nu iber of bus phases is equal to that of the sun ly r ains (Figs. 2, 4, 6) although individual reactor or power control unit will have to be larger in the former system (Fig. 7) than in the latter system (Figs. 2, 4, 6) for the same power requirements. On the other hand, systems with an equal number of sup ply and control phases (Figs. 2, 4, 6) have the aller or larger number advantage of a balanced multiphase load voltage, while in single-phase bus systems (Fig. 7) the phase distribution of the load voltage is greatly unbalanced, the corresponding phase distribution in a two-phase bus system being intermediate those of a single-phase bus system (Fig. 7) and a fully balanced multi-phase system (Figs. 2, 4, 6). Consequently, the choice of the preferred circuit design is somewhat governed by the requirements of each particular application, a three-phase system of a balanced design throughout (Figs. 2, 4, 6) being generally preferable, especially for multi-unit printing press drives, from the view point of most favorable load conditions to be imposed on the energizing power supply line.

While in the foregoing particular reference is made to printing press drives, it will be obvious that the invention is also applicable to multimotor control systems for other fabricating or processing plants in which a number of coacting machinery units are operated at correlated or equal drive speeds such as in box making and packaging plants, or wherever a web or strand material passes through aligned working units to be successively processed or acted upon as is the case, for instance, in the paper making industry, textile industry, steel or metal rolling mills, chemical or thermal processing plants, or multiple conveyor systems.

Furthermore, while I have shown system embodiments with two groups of motors capable of mutually independent operation, it need hardly be explained that various features of my invention are applicable with only a single group of a selectively variable number of motors and that the invention can equally well be applied to sys tems for three or more groups of motors having a corresponding number of mutually insulated single-phase or multi-phase buses.

It will also be obvious to those skilled in the art, upon a study of this disclosure, that systems according to my invention can readily be modified as regards their components, individual elements or circuit connections and hence may be embodied in designs other than those specifically shown and described, without departing from the objects and essential features of my invention and within the scope of the claims annexed hereto.

I claim:

1. A muiti-motor spec. control system, comprising of parallel connected induction motors, alternating-current supply means, condition-responsive voltage control means for controlling the speed of said motors having a group of selectively operable control sections interposed between said supply means and said motors, selector sr' tch means connected between said respective motors and said control means for selecting a desired number of said motors for simultaneous operation, and selector switch means connected with said control sections between said supp"- means and said motors for adapting the of operative control sections and thereby the current capacity of said control means to said number of motors.

2. A multi-motor speed control system, comprising a group of parallel connected induction motors, alternating-current supply means, controllabl impedance interposed between said supply means and said motors for controlling the speed of said motors and having a group of selectively operable impedance sections, first selector switch means connected between said respective motors and said impedance means for selecting a desired number of said motors for simultaneous operation, and second selector switch means connected with said impedance sections between said supply means and said first selector switch means for correlating the number of operative impedance sections and thereby the current capacity of said control means to said number of motors.

3. A multi-motor speed control system, comprising a group of parallel connected induction motors, alternating-current supply means, saturable reactor means interposed between said supply means and said motors for controlling the speed of said motors and having a group of selectively operable reactor sections, first selector switch means connected between said respective motors and said reactor means for selecting a desired number of said motors for simultaneous operation, and second selector switch means connected with said reactor sections between said supply means and said first selector switch means for adapting the number of operative sections and thereby the current capacity of said reactor means to said number of motors.

l. A multi-motor speed control system for a multi-unit printing press drive or the like, comprising a group or induction motors mechanically interconnectable for operation at a common speed, alternating-current supply means, a controllable impedance device interposed between said supply means and said group of motors for controlling the motor speed and having a group of selectively operable impedance sections, first selector switch means connected between said motors and said impedance device for selecting a desired number or" said motors for simultaneous operation, second selector switch means connected with said impedance sections between said supply means and said first selector switch means for adapting the number of operating impedance sections to said number of motors, said impedance device having impedance control means, and a control circuit connected with said control means and having voltage source means responsive to a speed-dependent operating condition of said motors to counteract departures or" said speed from a desired value.

5. A multi-motor speed control system for a multi-unit printing press drive or the like, comprising a group of induction motors mechanically interconnectable for operation at a common speed, alternating-current supply means, saturable reactor means interposed between said supply means and said group oi motors and having a group of selectively operable reactor sections, said reactor means having saturation control means for varying the reactance of said reactor means to thereby control said speed, first selector switch means connected between said motors and said reactor means for selecting a desired number of said motors for simultaneous operation, second selector switch means connected with said reactor sections between said supply means and said first selector switch means for adapting the number of operating reactor sections to said number of motors, and a control circuit connected with said saturation control means and having voltage supply means responsive to a load-dependent motor operating condition for regulating said speed.

6. A multi-motor speed control system for a multi-unit printing press drive or the like, comprising a group of induction motors mechanically interconnectable for operation at a common speed, alternating-current supply means, voltage control means interposed between said supply means and said group of motors and having a group of selectively operable control sections, said control means having a control circuit responsive to a motor operating condition for regulating said speed, first selector switch means connected between said respective motors and said control means for selecting a desired number of said motors for simultaneous operation, and second selector switch means connected with said control sections between said supply means and said first switch means and joined with said first switch means for setting the number oi operative control sections in a fixed relation to said selected number of motors, whereby the current capacity or said control means is automatically adapted to said number of motors.

7. A multi-motor speed control system a multi-unit printing press drive or the like, comprising a group of parallel arranged multi-p'nase induction motors, variable-voltage bus means, selective switch means connecting said respective motors with said bus means for selecting a desired number of said motors to be simultaneously energized through said bus means, multi-phase alternating-current supply mains, condition-responsive voltage control means disposed between said supply mains and said bus means for impressing controllable motor terminal voltage on said bus means to control the speed of said motors, said voltage control means having a group of selective sections, and selector switch means connected with said respective sections between said supply mains and said bus means for adapting the number of operative sections to said number of simultaneously energized motors.

8. A multi-motor speed control system for a multi-unit printing press drive or the like, comprising a group of parallel arranged multi-phase induction motors mechanically interconnectable for operation at a common speed, variable-voltage bus means, selector switch means connecting said respective motors with said bus means for selecting a desired number of said motors to be simultaneously energized through said bus means, alternating-current supply means, controllable impedance means having a group of impedance sections disposed between said supply means and said bus means for impressing controllable motor terminal voltage on said bus means to control the speed of said motors, said impedance sections having a common control circuit responsive to a motor operating condition for controlling said voltage and selector switch means connected with said respective sections between said supply means and said bus means for adapting the number of operative sections and thereby the current capacity of said impedance means to said number of simultaneously energized motors.

9. A multi-motor speed control system, comprising bus means, a group of induction motors parallel connected to said bus means, selector switch means series-connected with said respective motors for simultaneously energizing a selected number of said motors through said bus means, alternating-current supply means, condition-responsive impedance means having a group of impedance sections connected parallel to one another between said supply means and said bus means for controlling the speed of said motors, and selector switch means series connected with Said respective impedance sections for adapting is the number of operative sections to said number of motors.

10. A multi-rnotor control system, comprising bus means, a group of induction motors parallel connected to said bus means, selector switch means interposed between said respec we motors and said bus means for operating a selected number of said motors, al ernating-c lent supply means, a bani; or saturable reac rs having respective main windings connected parallel to one another between said supply means and said bus means and having respective saturation control air iings for 1 ying the impedance oi said res ective reactors, control circuit connected with said windin s and having variable-voltage supply means responsive to a motor operating condition, and selector switch means connected with said respective main windings between supply means and said bus means for adapting the number cf operative reactors to said number of motors.

ll. In a system according to claim 8, said impedance means comprising a saturable reactor having a main winding serially subdivided into said sections, and having a saturation control winding forming part of said control circuit.

12. A multi-motor speed control system for mu c-i-unit printing press drives or the like, comp ising first controllable alternating-current variable-voltage, constant frequency supply means and second controllable alternating-current variable-voltage, constant frequency supply means of individually controllable respective voltages, a first plurality of electric motors and appertaining respective switch means selectively parallel connecting said motors to said first supply means, a second plurality of electric motors and appertaining respective switch means selectively parallel connecting said latter motors to said second supply means, a third plurality of electric motors and appertaining respective selector switch means selectively parallel connecting said respective last-mentioned motors to a selected one of said two supply means, whereby a selected number of said third plurality of motors can operate together and at the same controlled voltage with a selected number of motors of either one of said first and second motor pluralities, said respective variable voltage supply m ans being controlled to maintain the speed of the motors connected to them, respectively, at predetermined values.

13. A multi-motor speed control system for multi-unit printing press drives or the like, cornprising first bus means and second bus means insulated from each other, a. first plurality of electric motors and appertaining selector switch means parallel connecting said respective motors to said first bus means, a second plurality of elec tric motors and appertaining selector switch means parallel connecting said respective latter motors to said second bus means, a third plurality of electric motors and appertaining selector switch means adapted for selectivel parallel connecting said respective last-mentioned motors to a selected one of said two bus means, constant frequency, alternating-current supply means for energizing said motors, first controllable impedance means of adjustable current capacity connecting said supply means with said first bus means for impressing controlled voltage on the group of selected motors connected to said first bus means to control the speed of said motors, second controllable impedance means of adjustable current capacity connecting said supply means with said second bus means for impressing prising first bus means and second bus means insulated from each other, a first plurality of induction motors and appertaining selector switch means parallel connecting a desired number of said motors to said first bus means, a second plurality of induction motors and appertaining selector switch means parallel connecting a desired number of said latter motors to said second bus means, a third plurality of electric motors and appertaining selector switch means parallel connecting a desired number of said last-mentioned A motors to a selected one of said two bus means, constant frequency, multi-phase alternating-current supply means for energizing said motors, first saturable reactor means of adjustable current capacity connecting said supply means with said first bus means for impressing controlled voltage on said first bus means to control the speed of the selected motors, second saturable reactor means of adjustable current capacity connecting said supply means with said second bus means for impressing controllable voltage on the selected group of motors connected to said second bus means to control the speed of the motors of said group, selective switch means connected with each of said reactor means between the appertaining bus means and said supply means for adapting said current capacit to said appertaining group of selected motors, each of said reactor means having saturation controlling circuit means provided with voltage supply means responsive to an operating condition of the appertaining motor group for controlling the reactance to counteract unwanted speed variations of said group.

15. In a multi-motor control system according to claim 14, said switch means of each of said motors being connected with one of said switch means of said respective reactor means so that any selection of the number of parallel operating motors is accompanied by a corresponding capacity adjustment of said reactor means.

16. In a multi-motor control system according to claim 14, each of said saturable reactor means comprising a number of individual reactors having respective main windings disposed in parallel relation to one another, and said selective switch means appertaining to said reactor means having respective switch units series connected with a plurality of said reactor main windings for selecting a number of parallel connected reactors in accordance with the desired current capacity.

17. In a multi-motor control system according to claim 14, each of said saturable reactor means comprising a number of winding sections series connected with one another between the appertaining bus means and said current supply means, and said selective switch means appertaining to said reactor means having contacts connected to respective reactor points between said sections.

18. A multi-motor speed control system for multi-unit printing press drives or the like, comprising first bus means and second bus means insulated from each other, a first plurality of induction motors and appertaining respective switch means selectively parallel connecting a desired number of said motors to said first bus means, a second plurality of induction motors and appertaining respective switch means selectively parallel connecting a desired number of said latter motors to said second bus means, a third plurality of electric motors and appertaining respective selector switch means parallel connecting a desired number of said last-mentioned motors to a selected one of said two bus means, multi-phase, constant frequency, alternatingcurrent supply means for energizing said motors, a first plurality of saturable reactors disposed in parallel between said supply means and said first bus means, a second plurality of saturable reactors disposed in parallel between said supply means and said second bus means, selectively actuable switches each being series-connected with one of said respective reactors of said first and second reactor pluralities, a third plurality of saturable reactors connected in parallel to said supply means and having respective selector switches attached to said first and second :bus means for connecting a selected number of said latter reactors with a selected one of said two bus means, all of said reactors having respective saturation control winding means, two control circuits each being responsive to an operating condition of the group of selected motors connected to one of said respective bus means and being attached to said control winding means of the group of selected reactors connected to said one bus means for counteracting unwanted speed variations of said group of motors.

19. In a multi-motor control system according to claim 18, the total number of said reactors in each of said reactor pluralities being equal to the total number of said motors in each of said respective motor pluralities.

20. In a multi-motor control system according to claim 18, said switch means of each of said motors being connected with one of said switches of said respective reactors so that any selection of the number of parallel operating motors is accompanied by the selection of an equal number of appertaining parallel operating reactors.

21. In a multi-motor control system according to claim 18, said control winding means of said first and second pluralities of reactors being connected with one and the other respectively of said two control circuits, and said control winding means of said third plurality of reactors having respective selector switches attached to both of said control circuits for connecting each of said latter control winding means with a selected one of said two circuits,

22. A multi-rnotor speed control system for a printing press drive, comprising a folder motor and a plurality of press motors mechanically interconnectable for operating a selected number of said press motors together with said folder motor, bus means, said motors being connected to said bus means in parallel relation to one another, switch means series-connected with said respective press motors for selectively energizing said selected number of press motors together with said folder motor, constant frequency, alternating current supply means, voltage control means connecting said supply means with said bus means for varying the bus potential to control the speed of said energized motors, speed responsive voltage supply means connected with said folder motor to provide a variable signal voltage, said control means having a control circuit connected with said voltage supply means 

